That's not an "AI tell". If you read anything in recent decades, this is a turn of speech human writers wrote for ages and still write.

"It's not just x, it's y." Absolutely clear tell, especially at this frequency. Examples from the article below:

"Over decades, it doesn’t just wear down, it also starts to run hot." "... the therapy didn’t just clear brain fog, it physically improved the brain’s ability to process and store information."

The quotes as well: "'... Not just living longer, but living smarter and healthier,' Shetty said." "'We aren’t just trying to understand the biological mechanisms, we are translating and developing our findings into real-world therapies that could make a difference,' Shetty said."

Anybody who still writes using their own mind has stopped using that pattern, along with others. "The thing nobody tells you:" is no longer used by decent writers.

It’s a tell now. I see it I assume AI and disregard.